Shuffle a Weighted array in Ruby

weighted.rb

def weighted
  a = []
  (1..60).each do |i|
    a << { value: "HIGH_#{i}", weight: 5 }
  end
  (1..30).each do |i|
    a << { value: "MID_#{i}", weight: 3 }
  end
  (1..15).each do |i|
    a << { value: "LOW_#{i}", weight: 2 }
  end
  a
end

def by_weight a, weight
  a.select{ |el| el[:weight] == weight }
end

def sum_of_weights weighted
  weighted.map{ |w| w[:weight] }.uniq.inject(:+).to_f
end

def probabilities weighted_array
  sum_of_weights = sum_of_weights(weighted_array)

  # initial probability
  probability = 0.0

  weights = weighted_array.map{ |w| w[:weight] }.uniq.sort
  weights.map do |w|
    current_probability = (w / sum_of_weights).round(3)
    # sum the current_probability with the previous
    probability += current_probability
    { weight: w, probability: probability }
  end
end

def get_weight probabilities
  r = rand
  probabilities.each do |p|
    return p[:weight] if r < p[:probability]
  end
end

def run
  # generate a weighted array
  a = weighted
  # calc the probabilities
  probabilities = probabilities a

  shuffle_weighted_array = []
  10.times do
    weight = get_weight probabilities
    shuffle_weighted_array << by_weight(a, weight).sample[:value]
  end

  shuffle_weighted_array
end

sums = {
  h: 0,
  m: 0,
  l: 0
}
1000.times do
  a = run
  sums[:h] += a.select{ |i| i[/^HIGH./] }.count
  sums[:m] += a.select{ |i| i[/^MID./] }.count
  sums[:l] += a.select{ |i| i[/^LOW./] }.count
end

# Prints the avarages of presence
p "HIGH AVG: #{sums[:h]/1000.0}"
p "MID AVG: #{sums[:m]/1000.0}"
p "LOW AVG: #{sums[:l]/1000.0}"